I was recently startled to find that the Earth's North Magnetic Pole is moving at upwards of 40 km per year, with an additional ~80 km daily elliptical drift about its mean position due to variations in solar wind. The Wikipedia article on the NMP has a wealth of information, including this image:
I'm particularly surprised at the existence of "modelled" data, showing a lot of detail, about the NMP's location for centuries before anyone went there. Neither that Wikipedia article nor this one on the Earth's magnetic field, which include the image, mention where the modelled data come from.
I get the impression from sources like this that the model is derived from historical measurements of magnetic declination. If that is the case I would be disinclined to trust the model much: the Earth's magnetic field has a complex enough structure that the magnetic north and south are not antipodal, with nontrivial spatial variations in magnetic declination at any given time.
Has anyone seen references that explain this model and what measurements they are based on?